The general objective in the treatment of gas streams from industrial and sewage plants is to combine, counteract, react and/or remove from such gas streams odorous constituents, such as volatile organic compounds (VOCs) and volatile inorganic compounds (VICs). It is well known in the prior art to remove odors from waste gases in liquid-gas reactions through absorption utilizing spray mist scrubber systems and packed bed scrubber systems. In conventional mist scrubber systems, an aqueous solution containing one or more chemicals reactive toward one or more of the odorous contaminants (typically an oxidizing compound and a hydroxide compound used for pH modification) is atomized to create liquid droplets which are dispersed into an odorous gas stream. The finely atomized liquid droplets absorb the malodorous compounds and allow oxidation of such odors, which removes them from the gas stream. The reaction vessels are constructed to provide desired absorption/reaction times for the odorous gas and the atomized aqueous/chemical fog, such absorption/reaction times typically range from about 5 to about 30 seconds or more for mist systems, and approximately 2 seconds for packed bed scrubbers.
These and other traditional approaches have in common either a relatively long contact time between the odorous gas and the treating liquid, in mist scrubbers, or for packed bed scrubbers, they use a relatively large volume of liquid per volume of gas treated. Conventional mist and packed bed scrubber systems can be inefficient with respect to the amount of chemical used. Moreover, these conventional systems tend to be large and are expensive to construct and operate.
In other conventional liquid-gas absorption processes, packed bed scrubber systems are utilized to provide large surface areas for the liquid-gas reaction to occur. However, packings used in packed bed scrubbers are often clogged by hard water, solid particulates and reaction by-products, negatively affecting the efficiency and overall function of such packed bed scrubber systems. Moreover, the size and expense of packed bed scrubber systems often preclude their use in many applications.
Problems in the treatment of sewage have also been encountered in the storage of sewage for extended periods of time. Among the problems, facultative bacteria present in sewage can react with sulfates in the absence of oxygen, thereby producing hydrogen sulfide, a malodorous poisonous gas, as well as other undesired odorous compounds. A combination of hydrogen sulfide gas with water vapor forms sulfuric acid, which causes deterioration of sewer pipes and sewer systems. Other undesirable compounds and gases may also form and need to be treated.
In conventional sewage systems, sewage is often held in various process apparatuses, such as a wet well, prior to treatment. Methods have been previously employed whereby chemicals are continuously fed into the wet well pump discharge line when the pump is operating or fed continually into the wet well. A continuous release system, however, may involve the undertreatment or overtreatment of sewage depending upon the time required for the wet well to fill to a predetermined level prior to evacuation. Alternatively, other systems treat malodorous sewage during the transport of such fluid from the wet well to other treatment containers. However, the sewage in the wet well prior to evacuation has the opportunity to ferment bacteria that produce undesirable, odoriferous compounds.
Another area of concern is the manner in which the sewage collection system, i.e., the collection of lines that convey sewage to a sewage treatment plant, is treated to inhibit the formation of undesirable chemicals or neutralize undesirable chemicals that have already formed. One presently known method for treating a sewage collection system is to manually dispense a sewage treatment chemical at various locations in the system. This method is typically labor intensive and generally makes relatively inefficient and sometime ineffective use of the sewage treatment chemical. Another known method of treating a collection system involves the use of a plurality of independent dispensers dispersed throughout the system with each dispenser continuously dispensing a sewage treatment chemical into the system. These systems also tend to make relatively inefficient and many times ineffective use of the sewage treatment chemical. Consequently, there is a need for a method and/or apparatus for chemically treating a sewage collection system that addresses the deficiencies of the known treatment systems.